Sole for an Athletic Shoe

ABSTRACT

In the sole, inequalities, m 2≥ m 1,  m 1≥ f and m 1 ≥h are satisfied, wherein the rearmost end of the foot-sole-contact-side surface is set to the origin, the path measured along the surface from the origin to the tip of the toe is set to L, the sole thicknesses at the positions of Sh(0.16×L), Sm 2  {(0.3-0.5)×L}, Sm 1 {(0.4−0.6)×L} and Sf(0.7×L) are set to h, m 2,  m 1  and f, respectively. An inequality, θ2&gt;θ1 is satisfied, wherein the angle between the line connecting the positions Sm 1 , Sh and the horizontal plane is set to θ1, and the angle between the line connecting the positions Sm1′, Sh′ and the horizontal plane is set to θ2, in which the position where the vertical lines drawn from the positions Sm 1 , Sh cross the ground-contact surface are set to Sm1′, Sh′, respectively. The ground-contact surface has a downwardly convexly curved shape at the forefoot region.

BACKGROUND OF THE INVENTION

The present invention relates generally to a sole for an athletic shoe, and more particularly, to an improvement in a sole structure so as to promote a ground contact at a forefoot region or a midfoot region at the time of impacting the ground and achieve a forefoot running style or a midfoot running style with ease.

Recently, when running fast in a long-distance race, a forefoot running style that impacts the ground at the forefoot region or a midfoot running style that impacts the ground at the midfoot region has become mainstream. The forefoot running style and the midfoot running style have merits that they are superior in shock absorbance, reduce a load on a body of a shoe wearer, and stabilize a trunk of the body because they impact the ground at a large area of a foot sole. However, these running styles require skills above a certain skill level. Therefore, it is not easy for beginners or unskilled runners to learn these running styles.

Japanese patent application publication No. 2018-78968 (hereinafter referred to as '968) discloses a sole in which the thicknesses of the heel portion and the forefoot portion of the sole are made constant respectively, the thickness of the forefoot portion is made greater than the thickness of the heel portion, and the thickness of the midfoot region is made gradually greater toward the forefoot portion. The publication '968 describes that the distance of the gravity center movement becomes longer during running to obtain a larger propulsion and thus increase a running speed (see paras. [0013] to [0016] and FIG. 2).

Also, Japanese patent application publication No. 2001-186904 (hereinafter referred to as '904) discloses an article of footwear in which a bulged portion is provided at a position corresponding to a thenar eminence, the sole is formed by a gentle continuous curve from the bulged portion to the toe portion and there is no depressions formed from the arch portion to the bulged portion (see para. [0016] and FIGS. 1 to 4). The publication '904 describes that an impact load to the thenar eminence or the toe portion at the time of impacting the ground can be relieved and the burden on muscles can be reduced.

Moreover, Japanese patent application publication No. 2002-336005 (hereinafter referred to as '005) discloses a shoe without a heel in which the thickness of the sole is made thicker at the midfoot region and the sole at the forefoot region is made flat (see FIG. 2)

However, in the above-mentioned structures shown in the publications '968 and '904, there are no regulating means to regulate the gravity center movement toward the heel portion after impacting the ground at the forefoot portion. Therefore, runners need skills in order to stably impact the ground at the forefoot portion. Also, in the above-mentioned structure shown in the publication No. '005, it is also difficult to stably impact the ground at the forefoot portion because the sole of the forefoot portion is not so structured as to roll forward toward the toe portion.

The present invention has been made in view of these circumstances and its object is to provide a sole for an athletic shoe that can promote a ground contact at a forefoot region or a midfoot region at the time of impacting the ground and that can achieve a forefoot running style or a midfoot running style with ease.

Other objects and advantages of the present invention will be obvious and appear hereinafter.

SUMMARY OF THE INVENTION

A sole for an athletic shoe according to the present invention extends from a heel region through a midfoot region and a forefoot region to a toe portion and has a foot-sole-contact-side surface on an upper side of the sole and a ground-contact surface on a lower side of the sole. With regard to dimensions of the sole, inequalities, m2≥m1, m1≥f and m1≥h are satisfied, wherein a position of a rearmost end of the foot-sole-contact-side surface is set to the origin of a coordinate, a path length measured along the foot-sole-contact-side surface from the origin to a tip of a toe is set to L, with the foot-sole-contact-side surface at the heel region arranged parallel to a horizontal plane, a thickness of the sole at a position Sh of a distance of 0.16×L away from the origin is set to h, a thickness of the sole at a position Sm2 of a distance of (0.3−0.5)×L away from the origin is set to m2, a thickness of the sole at a position Sm1 of a distance of (0.4-0.6)×L away from the origin is set to m1 provided that the position Sm1 is disposed in front of the position Sm2, and a thickness of the sole at a position Sf of a distance of 0.7×L away from the origin is set to f.

Also, an inequality, θ2>θ1 is satisfied, wherein an angle between a line connecting the positions Sm1 and Sh and the horizontal plane is set to θ1, a position where a vertical line drawn from the position Sm1 crosses a ground-contact surface is set to Sm1′, a position where a vertical line drawn from the position Sh crosses the ground-contact surface is set to Sh′, and an angle between a line connecting the positions Sm1′ and Sh′ and the horizontal plane is set to θ2. The ground-contact surface has a downwardly convexly curved shape at the forefoot region.

According to the present invention, the sole thickness h at the position Sh of the distance of 0.16×L away from the origin, i.e. a heel center, is smaller than the sole thickness m1 at the position Sm1 of the distance of (0.4-0.6)×L away from the origin, and besides, the angle θ2 between the line connecting the positions Sm1′ and Sh′ and the horizontal plane is greater than the angle θ1 between the line connecting the positions Sm1 and Sh and the horizontal plane. Therefore, at the time of striking onto the ground, the heel region does not come into contact with the ground and thus a heel strike will not occur. As a result of this, a forefoot contact or a midfoot contact with the ground can be promoted at the time of a ground contact.

Also, the sole thickness m2 at the position Sm2 is greater than the sole thickness ml at the position Sm1. Thereby, when the ground-contact surface comes into an initial contact with the ground at the position Sm1′, the sole can be restricted from inclining rearwardly to cause the heel region to move downwardly. As a result, a smooth transfer from the initial contact with the ground to a forward rolling of the sole can be achieved.

Moreover, the sole thickness fat the position Sf of the distance of 0.7×L away from the origin, i.e. the center of the thenar eminence is smaller than the sole thickness ml at the position Sm1 of the distance of (0.4-0.6)×L away from the origin, and besides, the ground-contact surface of the sole has a downwardly convexly curved shape at the forefoot region. Thereby, a forward rolling of the sole can be conducted smoothly. In such a manner, a forefoot running style or a midfoot running style can be achieved with ease.

With regard to the sole thickness t at the tip of the toe, an inequality, t>≤f/2 may be satisfied. Thereby, a forward rolling of the sole toward the tip of the toe can be conducted in a smoother manner.

The sole may further comprise a plate that extends in the longitudinal direction in the sole. The front end of the plate may be disposed on the ground-contact side below the sole thickness centerline at the forefoot region, the rear end of the plate may be disposed on the foot-sole-contact side above the sole thickness centerline at the heel region, and the mid-portion of the plate may cross the sole thickness centerline diagonally at the midfoot region.

According to the present invention, when a load is transferred toward the front end of the plate after an initial contact with the ground, it can be securely restricted by the plate that the sole inclines rearwardly to cause the heel region to move downwardly. As a result, a smoother transfer from the initial contact with the ground to a forward rolling of the sole can be achieved.

The plate may have a bulged portion that protrudes in a vertical direction at least at a part of a region extending from the position Sm2 to the position Sf. The bulged portion can increase the bending rigidity of the plate. Thereby, a downward movement of the heel region after the initial contact with the ground can be more securely restricted.

As explained above, in accordance with the sole for an athletic shoe of the present invention, a forefoot contact or a midfoot contact with the ground can be promoted at the time of a ground contact, such that thereby a forefoot running style or a midfoot running style can be achieved with ease.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention.

FIG. 1 is a general lateral side view of an athletic shoe employing a sole according to an embodiment of the present invention.

FIG. 2 is a general bottom view of the shoe of FIG. 1.

FIG. 3 is a sectional view of FIG. 2 taken along line III-III illustrating a longitudinal sectional view along a longitudinal centerline of the shoe of FIG. 1.

FIG. 4 is a cross sectional view of FIG. 2 taken along line IV-IV.

FIG. 5 is a cross sectional view of FIG. 2 taken along line V-V.

FIG. 6 is a cross sectional view of FIG. 2 taken along line VI-VI.

FIG. 7 is a cross sectional view of FIG. 2 taken along line VII-VII.

FIG. 8 is an exploded view of the shoe of FIG. 1.

FIG. 9 is an enlarged view of FIG. 3, showing the details of the sole of the shoe of FIG. 1 and illustrating a last of the shoe as well.

FIG. 10 shows the state of the shoe of FIG. 1 during running, illustrating the motion of the shoe relative to the ground in order of (a) to (d) in time-series manner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings. FIGS. 1 to 10 show a sole of an athletic shoe according to an embodiment of the present invention. Here, a running shoe for a middle distance is taken for an example.

In the following explanation, “upward (upper side/upper)” and “downward (lower side/lower)” designate an upward direction and a downward direction, or vertical direction, of the shoe, respectively, “forward (front side/front)” and “rearward (rear side/rear)” designate a forward direction and a rearward direction, or longitudinal direction, of the shoe, respectively, and “a width or lateral direction” designates a crosswise direction of the shoe.

For example, in FIG. 1, a general lateral side view of the shoe, “upward” and “downward” designate “upward” and “downward” in FIG. 1 respectively, “forward” and “rearward” designate “left to right direction” in FIG. 1 and “a width direction” designates “out of the page” and “into the page” of FIG. 1. Similarly, in FIG. 2 a general bottom view of the sole, “upward” and “downward” designate “into the page” and ^(“)out of the page” of FIG. 2 respectively, “forward” and ^(“)rearward” designate “upward” and “downward” in FIG. 2, and “a width direction” designates “left to right direction” in FIG. 2.

As shown in FIG. 1, Shoe 1 comprises a sole 2 and an upper 10 provided on the sole 2. The sole 2 includes an upper midsole 3 disposed on an upper side of the sole 2, a lower midsole 4 disposed on a lower side of the sole 2, and an outsole 5 attached on a bottom surface of the lower midsole 4 and having a ground-contact surface 58 on a bottom side that contacts the ground. These upper and lower midsoles 3, 4 and the outsole 5 are integrated to form the sole 2. The upper 10 has a tongue portion 11 at an upper-side aperture of the shoe 1.

As shown in FIGS. 1 and 3, the upper midsole 3 extends from a heel region through a midfoot region and a forefoot region to a toe portion of the sole 2, i.e. over an entire length of the sole 2, in a longitudinal direction. The lower midsole 4 is disposed mainly at a rearfoot region (that is, a region including the heel region and the midfoot region) of the sole 2 and is not provided at the toe in the forefoot region (see FIG. 4, a cross sectional view of FIG. 2 taken along line IV-IV).

As shown in FIGS. 3 and 8, between the upper midsole 3 and the lower midsole 4, a plate 6 is provided. The plate 6 is a thin sheet-like member that extends from the heel region to the toe of the sole 2 in the longitudinal direction. A thickness of the plate 6 is for example, approximately 1 to 2 mm. At the heel region and the midfoot region of the sole 2, the plate 6 is sandwiched between a lower surface 3B of the upper midsole 3 and an upper surface 4A of the lower midsole 4 (see FIGS. 5 to 8). At the forefoot region of the sole 2, the plate 6 is sandwiched between the lower surface 3B of the upper midsole 3 and an upper surface 5A of the outsole 5 (see FIG. 4).

As shown in FIGS. 5 and 6, the plate 6 has a bulged portion 60 that bulges or protrudes upwardly in an arch-shape or a generally inverted V-shape at the midfoot region of the sole 2. The plate 6 is depressed in an inverted arch-shape or a V-shape on opposite sides of the bulged portion 60. The inverted V-shaped bulged portion 60 and the opposite-side V-shaped portions of the bulged portion 60 form a wavy corrugated shape. A ridge line and a through line of such a wavy corrugated shape extend in the longitudinal direction at the midfoot region of the sole 2. As shown in FIGS. 4 and 7, the plate 6 is generally planar in shape at the forefoot region and the heel region of the sole 2.

The upper midsole 3 and the lower midsoles 4 are formed of a soft elastic material, more specifically, thermoplastic synthetic resin and its foamed resin such as ethylene-vinyl acetate copolymer (EVA) or the like, thermosetting synthetic resin and its foamed resin such as polyurethane (PU) or the like, alternatively, rubber material and foamed rubber such as butadiene rubber, chloroprene rubber or the like.4

The plate 6 is formed of thermoplastic resin comparatively rich in elasticity such as thermo plastic polyurethane (TPU), polyamide elastomer (PAE), acrylonitrile butadiene styrene resin (ABS) and the like, alternatively, thermosetting resin such as epoxy resin, unsaturated polyester resin and the like. Also, as a material for the plate 6, fiber reinforced plastics (FRP) may be adopted in which carbon fibers, aramid fibers, glass fibers or the like are incorporated as a strengthened fiber, and thermosetting resin or thermoplastic resin is incorporated as matrix resin.

The outsole 5 is formed of hard elastic materials, more specifically, thermoplastic resin such as thermoplastic polyurethane (TPU), polyamideelastomer (PAE) and the like, thermosetting resin such as epoxy resin and the like, or solid rubber.

Next, the dimensions of the respective parts of the sole 2 will be explained in more detail with reference to FIG. 9.

FIG. 9 corresponds to FIG. 3 and is a longitudinal sectional view along a longitudinal centerline of the sole 2. Here, hatching is omitted for illustration purposes. FIG. 9 also shows the state in which a last 100 is inserted into the upper 10. A bottom surface of the last 100 is in contact with a foot-sole-contact-side surface 3A of the upper midsole 3, which constitutes an upper surface of the sole 2.

As shown in FIG. 9, inequalities, and m1≥h are satisfied, wherein a position Se of a rearmost end of the foot-sole-contact-side surface 3A of the upper midsole 3 is set to the origin of a coordinate, a path length measured along the foot-sole-contact-side surface 3A from the origin to a position St of a tip of a toe, which corresponds to a path length along a bottom surface of a last 100 is set to L, with the foot-sole-contact-side surface 3A at the heel region, which corresponds to a heel bottom surface, arranged parallel to a horizontal plane Hp, a thickness of the sole at a position Sh of a distance of 0.16×L away from the origin, which corresponds to a heel central position, is set to h, a thickness of the sole at a position Sm2 of a distance of (0.3-0.5)×L away from the origin is set to m2, a thickness of the sole at a position Sm1 of a distance of (0.4-0.6)×L away from the origin is set to m1 provided that the position Sm1 is disposed in front of the position Sm2, and a thickness of the sole at a position Sf of a distance of 0.7×L away from the origin, which corresponds to a center of a thenar eminence, is set to f.

Here, in this embodiment, since the sole 2 is composed of the upper midsole 3, the lower midsole 4 and the outsole 5, the thickness of the sole at the respective portions designates a total thickness of the sole that includes the upper midsole 3, the lower midsole 4 and the outsole 5.

The position Sm1 corresponds to a position of an initial ground contact at the time of impacting the ground during running. The inequality, m2≥m1 means that the sole thickness at the rear of the position of the initial ground contact is equal to or greater than the sole thickness of the position of the initial ground contact. That is for preventing the heel region of the sole 2 from moving downwardly after the initial ground contact. The sole thickness m2 at the position Sm2 demonstrates a “supporting stand” effect to support a load at the position Sm2 after the initial ground contact at the position Sm1. Thereby, when the sole 2 is going to lean toward the heel region after the initial ground contact and a shift or a travel of a center of gravity to the rear is going to occur, such a travel of the center of gravity is restricted and time for travel of the center of gravity to the rear can be made as short as possible. As a result, after the initial ground contact, a load transfer to the forward can be conducted in a prompt manner.

The inequality, m1≥f is for the center of gravity to move easily in a forward direction after the initial ground contact to promote a forward rolling. The inequality, m1≥h is for preventing the heel region of the sole 2 from contacting the ground at the time of a sole contact with the ground to keep the heel region apart from the ground surface to promote a ground contact at the forefoot region.

Also, as shown in FIG. 9, an inequality, θ2>θ1 is satisfied, wherein an angle between a line connecting the positions Sm1 and Sh and a horizontal plane Hp is set to el, a position where a vertical line drawn from the position Sm1 crosses a ground-contact surface 5B is set to Sm1′, a position where a vertical line drawn from the position Sh crosses the ground-contact surface 5B is set to Sh′, and an angle between a line connecting the positions Sm1′ and Sh′ and the horizontal plane Hp is set to θ2. That is also for preventing the heel region of the sole 2 from contacting the ground at the time of the sole contact with the ground to keep the heel region apart from the ground surface to promote the ground contact at the forefoot region.

The ground-contact surface 5B has a downwardly convexly curved shape, for example a gently round shape, at the forefoot region of the sole 2. That is for promoting a forward rolling of the sole 2 after the initial ground contact. Also, preferably, an inequality, t≤f/2 is satisfied wherein a thickness of the sole 2 at the position St of the tip of the toe is set to t. That is for promoting a forward rolling of the sole 2 toward the tip of the toe after the initial ground contact.

In the present embodiment, as specific values of the sole thicknesses, m1, m2, h and f, preferably, the following values are employed:

-   -   m1≥15 [mm];     -   m2≥16 [mm];     -   h≥10 [mm]; and     -   f≥10[mm].

As shown in FIG. 9, a front end portion of the plate 6 is disposed on the side of a ground-contact surface 5B below a sole thickness centerline Sc at the forefoot region, a rear end portion of the plate 6 is disposed on the side of the foot-sole-contact surface 3A above the sole thickness centerline Sc at the rearfoot region, and a mid-portion of the plate 6 crosses the sole thickness centerline Sc diagonally at the midfoot region. Here, the sole thickness centerline Sc is a line connecting a center of the total thickness of the sole 2 in the longitudinal direction as shown in FIG. 9. Also, the bulged portion 60 of the plate 6 is provided at least at a part of a region extending from the position Sm2 to the position Sf, that is, a region of (0.3-0.7)×L.

Then, effects of the present embodiment will be explained using FIG. 10 in reference to FIG. 9.

FIG. 10(a) shows a phase immediately before a ground contact of the sole 2. Arrow F in FIG. 10 (a) designates the direction of movement of the sole 2. At this time, the heel region of the sole 2 is kept apart from the ground surface R. The sole 2 is going to come into contact with the ground surface R from the position at the sole thickness ml. That is because the inequalities m1≥h and θ2≥θ1 (see FIG. 9) are satisfied in the sole 2 as above-mentioned, the heel region of the sole 2 is thus thinner, and consequently, when the shoe 1 impacts the ground the sole 2 is going to contact the ground not from the heel region but from the midfoot region.

FIG. 10(b) shows a phase in which the sole 2 comes into an initial contact with the ground surface R at the position of the sole thickness m1. At this time, the inequality m2≥m1 is satisfied in the sole 2 as above-mentioned, the sole thickness m2 at the rear of the position of the initial ground contact is at least equal to or greater than the sole thickness m1 at the position of the initial ground contact. Thereby, a downward sinking movement of the heel region of the sole 2 immediately after the initial ground contact is supported by the position of the thickness m2 having a greater thickness than the position of the thickness m1. Thereby, such a rearward movement toward the heel region of the sole 2 can be restricted. As a result, when the sole 2 is about to lean to the heel region after the initial ground contact and the movement of the center of gravity to the rear is thus going to occur, the time for such a rearward travel of the center of gravity can be made as short as possible and thereby a prompt load transfer in the forward direction after the initial ground contact can be conducted.

FIG. 10(c) shows a phase in which the forefoot region of the sole 2 comes into contact with the ground. At this time, since the inequality, m1≥f is satisfied as above-mentioned, the sole 2 is easy to move onto a forward load transfer after the initial ground contact and a forward rolling can thus be promoted. Moreover, in this case, since the ground-contact surface 5B has a downwardly convexly curved surface, the sole 2 is easy to roll in the forward direction after the initial ground contact.

Also, in this case, when the weight of a shoe wearer moves to the forefoot region, the front end portion of the plate 6 is pressed downwardly and the central portion and the heel portion of the plate 6 can thus hold the weight of the wearer firmly. As a result, a downward sinking movement of the midfoot region and the heel region of the sole 2 can be prevented and a load transfer to the forefoot region can thus be conducted in a smooth manner.

Furthermore, in this case, since the bulged portion 60 is formed at a central portion of the plate 6, the bending rigidity of the central portion is high. Therefore, the downward sinking movement of the midfoot region and the heel region of the sole 2 can be prevented further securely, such that thereby a weight transfer to the forefoot region can be conducted more smoothly.

FIG. 10(d) shows a phase of push-off motion of the toe. At this juncture, since the sole thickness t at the position St of the tip end of the toe satisfies the inequality, t≤f/2, a forward rolling toward the tip end of the toe can be promoted. Also, in this case, since the midfoot portion and the heel portion of the foot is supported by the plate 6, at the time of the push-off motion of the toe, the wearer can obtain an action of elastic repulsion of the plate 6. Thereby, the wearer can strike the ground surface R strongly to acquire a driving force.

Alternative Embodiment

In the above-mentioned embodiment, an example was shown in which the sole 2 for the athletic shoe 1 is formed of the upper midsole 3, the lower midsole 4, the outsole 5 and the plate 6, but the present invention is not limited to such an example. The present invention also has application to a sole without a plate 6. In that case, the upper midsole 3 and the lower midsole 4 may be formed of one-piece midsole.

As mentioned above, the present invention is useful for a sole for an athletic shoe that can promote a ground contact at the forefoot region or the midfoot region at the time of impacting the ground to achieve a forefoot running style or a midfoot running style with ease.

Those skilled in the art to which the invention pertains may make modifications and other embodiments employing the principles of this invention without departing from its spirit or essential characteristics particularly upon considering the foregoing teachings. The described embodiments and examples are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. Consequently, while the invention has been described with reference to particular embodiments and examples, modifications of structure, sequence, materials and the like would be apparent to those skilled in the art, yet fall within the scope of the invention. 

What is claimed is:
 1. A sole for an athletic shoe, said sole extending from a heel region through a midfoot region and a forefoot region to a toe portion and having a foot-sole-contact-side surface on an upper side of said sole and a ground-contact surface on a lower side of said sole, wherein inequalities, m2≥m1, m1≥f and m1≥h are satisfied, in which a position of a rearmost end of said foot-sole-contact-side surface is set to the origin of a coordinate, a path length measured along said foot-sole-contact-side surface from the origin to a position of a tip of the toe is set to L, with said foot-sole-contact-side surface at said heel region arranged parallel to a horizontal plane, a thickness of said sole at a position Sh of a distance of 0.16×L away from the origin is set to h, a thickness of said sole at a position Sm2 of a distance of (0.3-0.5)×L away from the origin is set to m2, a thickness of said sole at a position Sm1 of a distance of (0.4-0.6)×L away from the origin is set to m1 provided that the position Sm1 is disposed in front of the position Sm2, and a thickness of said sole at a position Sf of a distance of 0.7×L away from the origin is set to f, wherein an inequality, θ2≥θ1 is satisfied, in which an angle between a line connecting the positions Sm1 and Sh and said horizontal plane is set to θ1, a position where a vertical line drawn from the position Sm1 crosses a ground-contact surface is set to Sm1′, a position where a vertical line drawn from the position Sh crosses said ground-contact surface is set to Sh′, and an angle between a line connecting the positions Sm1′ and Sh′ and said horizontal plane is set to θ2, and wherein said ground-contact surface has a downwardly convexly curved shape at said forefoot region.
 2. The sole according to claim 1, wherein an inequality, t≤f/2 is satisfied wherein a thickness of said sole at said tip of said toe is set to t.
 3. The sole according to claim 1 further comprising a plate provided in said sole and extending in a longitudinal direction, said plate comprising a front end, a rear end and a mid-portion disposed between said front end and said rear end, wherein said front end of said plate is disposed on a ground-contact side below a sole thickness centerline at said forefoot region, said rear end of said plate is disposed on a foot-sole-contact side above said sole thickness centerline at said heel region, and said mid-portion of said plate crosses said sole thickness centerline diagonally at said midfoot region.
 4. The sole according to claim 3, wherein said plate has a bulged portion that protrudes in a vertical direction at least at a part of a region extending from the position Sm2 to the position Sf. 